1. Field of the Invention
The present invention relates to a magnetostatic wave element. More specifically, it relates to a magnetostatic wave element which, for example, converts microwaves into magnetostatic waves which propagate through a single crystal magnetic garnet film and further converts the magnetostatic waves into microwaves for output, as well as to a manufacturing method therefor.
2. Description of the Related Art
FIG. 1 is an illustrative view showing an example of a magnetostatic wave element which is art related to the present invention. A magnetostatic wave element 10 contains a non-magnetic substrate 12. A gadolinium-gallium-garnet (GGG) substrate or the like is used as the non-magnetic substrate 12, for example. A single crystal magnetic garnet film 14 is formed on the non-magnetic substrate 12. An yttrium-iron-garnet (YIG) film or the like is used as the single crystal magnetic garnet film 14. Furthermore, two microstrip lines 16 and 18 are formed on the single crystal magnetic garnet film 14 at a specific distance apart. Microstrip line 16 is used for signal input and microstrip line 18 is used for signal output.
When such an magnetostatic wave element 10 is used, a magnetic field H is applied, for example, in the direction parallel to the microstrip lines 16 and 18. Accordingly, when a microwave signal is input at one of the microstrip lines such as microstrip line 16, it is converted to a magnetostatic wave and the magnetostatic wave propagates through the single crystal magnetic garnet film 14. Then it is converted to microwaves at the other microstrip line 18 and is output as a microwave output signal.
With such a magnetostatic wave element, when an input signal with an electric power Pin which is not less than Psh is input at a frequency fo, a signal with an electric power which is smaller than that of the input signal by the value of Pin-Psh is output only for the region of frequency fo as shown in FIGS. 2A and 2B. An S/N enhancer, a limiter, etc., may be manufactured utilizing this behavior.
Thus, this magnetostatic wave element provides an output signal with an electric power smaller than that of the input signal at frequency fo. There is also observed a phenomenon in which an output signal is suppressed for an input signal with an electric power smaller than Psh in a frequency region which is smaller or larger than fo. Although an output signal is preferably not suppressed for an input signal with an electric power not more than Psh in practice, there is such a phenomenon in reality, degrading the properties of a magnetostatic wave element.
In general, a magnetostatic wave element which has good properties has desirably a narrow bandwidth range in which an output signal is suppressed for an input signal with an electric power not more than Psh. That is, a magnetostatic wave element with a narrow bandwidth range Ba is preferable, when a bandwidth range in which an output signal is suppressed centering around frequency fo by 3 dB or more, is represented by Ba as shown in FIGS. 2A and 2B.
Accordingly, it is an object of the present invention to provide a magnetostatic wave element having a narrow bandwidth range Ba in which an output signal is suppressed centering around frequency fo by 3 dB or more for an input signal with an electric power not more than Psh, as well as to provide a manufacturing method therefor.
Various aspects of the present invention are described as follows.
(1) According to the present invention, a magnetostatic wave element comprising a single crystal magnetic garnet film is manufactured, wherein the film contains about 5 ppm or less by weight of Pb.
(2) In such a magnetostatic wave element, the single crystal magnetic garnet film can be formed on a non-magnetic substrate by the liquid phase epitaxial method.
(3) Furthermore, the single crystal magnetic garnet film can be formed by the liquid phase epitaxial method using a raw material comprising MoO3.
(4) Furthermore, the single crystal magnetic garnet film can be an yttrium-iron-garnet-based single crystal film.
(5) Furthermore, the single crystal magnetic garnet film can comprise two microstrip lines located on the film and approximately in parallel with each other with a specific distance therebetween.
(6) According to the present invention, such an element is manufactured by a method for manufacturing a magnetostatic wave element having a single crystal magnetic garnet film, comprising the steps of:
preparing a raw material by melting into a solvent having a molybdenum oxide as the principal component and being substantially Pb-free, a single crystal film forming component for forming the single crystal magnetic garnet film; and
bringing this raw material into contact with a seed substrate to grow a single crystal magnetic garnet film with a Pb content of about 5 ppm or less by weight on the seed substrate.
(7) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (6), wherein the molybdenum oxide is MoO3.
(8) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (6), wherein the solvent further comprises an alkali metal oxide.
(9) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (8), wherein the solvent comprises about 50-90 mol % of the molybdenum oxide, and about 10-50 mol % of the alkali metal oxide.
(10) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (6), wherein the single crystal film forming component is a component of an yttrium-iron-garnet system.
(11) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (6), wherein the seed substrate is a non-magnetic substrate.
(12) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (11), wherein the non-magnetic substrate is a substrate made of a gadolinium-gallium-garnet system.
(13) According to the present invention, such an element is also manufactured by a method for manufacturing a magnetostatic wave element as set forth in the above-described (6), wherein two microstrip lines are formed on the single crystal magnetic garnet film and approximately in parallel with each other at a specific distance therebetween.
A single crystal magnetic garnet film formed on a non-magnetic substrate by the liquid phase epitaxial method is mainly used for a magnetostatic wave element. To form a single crystal magnetic garnet film on a non-magnetic substrate, a solution of a single crystal film forming component melted as a solute in a solvent component is supersaturated, and the solution is brought into contact with a rotating non-magnetic substrate so as to grow a single crystal on the non-magnetic substrate. According to the most common methods, a Pb compound is used as one of the components for the solvent. Therefore, the single crystal magnetic garnet film thus manufactured comprises Pb which is not an element for constituting the magnetic garnet.
As a result of research to study the relationship between the content of Pb contained in a single crystal magnetic garnet film and the bandwidth range Ba in which an output signal was suppressed centering around frequency fo by 3 dB or more, it was found that Ba became narrower when there was a lower content of Pb, as shown in FIG. 3. Thereupon, it was supposed that a magnetostatic wave element having good properties could be obtained if the single crystal magnetic garnet film was substantially Pb-free, and the present invention has been achieved accordingly. It is noted that the content of Pb is specified to be about 5 ppm or less by weight, since the limit of detection of the inductively coupled plasma emission spectroscopy is about 5 ppm by weight for measuring the content of Pb contained in a single crystal magnetic garnet film.
The above-described purpose, other purposes, features and advantages of the present invention will be further clarified by the detailed description of the following embodiments of the invention with reference to the drawings.
According to the present invention, the bandwidth range Ba in which the electric power of an output signal is suppressed centering around frequency fo by 3 dB or more, can be narrowed by virtue of a Pb content of about 5 ppm or less by weight contained in a single crystal magnetic garnet film formed on a non-magnetic substrate. As a result, a magnetostatic wave element having good frequency properties can be obtained. Therefore, it is now possible to use this magnetostatic wave element in manufacturing an S/N enhancer or a limiter with good properties.